Various forms of network storage systems exist today, including network attached storage (NAS), storage area networks (SANs), and others. Network storage systems are commonly used for a variety of purposes, such as backing up critical data, providing multiple users with access to shared data, etc.
A network storage system includes at least one storage server, which is a processing system configured to store and retrieve data on behalf of one or more client processing systems (“clients”). In the context of NAS, a storage server is commonly a file server, which is sometimes called a “filer”. A filer operates on behalf of one or more clients to store and manage shared files. The files may be stored in a storage subsystem that includes one or more arrays of mass storage devices, such as magnetic or optical disks or tapes, by using RAID (Redundant Array of Inexpensive Disks). Hence, the mass storage devices in each array may be organized into one or more separate RAID groups.
In a SAN context, a storage server provides clients with access to stored data at a sub-file level of granularity, such as block-level access, rather than file-level access. Some storage servers are capable of providing clients with both file-level access and block-level access, such as certain Filers made by Network Appliance, Inc. (NetApp®) of Sunnyvale, Calif.
As noted above, backing up data is a common use of a network storage system. There is a particular need for good backup solutions for network storage at the enterprise level, particularly (though not exclusively) for small and medium businesses (SMBs). Many SMB users do not want to invest in or maintain separate backup software, servers and systems, and do not have effective operational processes for managing data or media. Such users want an easy-to-use, integrated solution for disaster recovery (DR) or archiving data, which can be set up and operated by office staff or information technology (IT) generalists.
In this context, it is often desirable to have an easy-to-use, cost-effective data backup solution for network storage, according to which backup copies of the primary data are stored “offsite”, i.e., at a location which is remote with respect to the location of the primary data. Further, it is often desirable to have such a solution which is also reliable, easily portable and which enables relatively fast storage and retrieval of data.
Various backup solutions for network storage are known, all of which have shortcomings relative to the above-noted criteria. For example, one possible approach is to provide a complete mirroring system at a remote site, to mirror the data at the primary site. The mirroring system includes a separate storage server and accompanying storage devices (e.g., disks). Consequently, this approach tends to be expensive and is not very portable.
Another common approach is to save backup copies of data onto tapes. This solution requires separate tape drives and, therefore, also tends to be expensive and not very portable. In addition, tape drives tend to be slower and less robust than disk drives, which are typically used for primary storage.
Other known approaches to data backup include those designed for use on individual personal computers (PCs). For example, recent versions of the Microsoft Windows operating system have the ability to generate a point-in-time image of a particular drive (e.g., the “C:” drive) onto another drive. This approach and other approaches designed for use on individual PCs are not suitable for use on a large-scale, in network storage systems.